Method and apparatus for diffusion coating of metals in coiled strips



Dec. 5, 1967 T GIBSON ETAL 3,356,523

' METHOD AND APPARATUS FOR DIFFUSION COATING 0F METALS IN COILED STRIPS Filed Nov. 14, 1963 5 Sheets-Sheet 1 6 O I n e v H I y m AW $5 K M M m Z nw 3 Sheets-Sheet 2 lnvenlors Attorney u umi SJ 77/0/4115 G/aso/v mo W/LLMM R. NGADAM T. GIBSON ETAL METHOD AND APPARATUS FOR DIFFUSION COATING OF METALS IN COILED STRIPS 1963 Dec. 5, 1967 Filed Nov. 14,

Dec. 5,1967 T. GIBSON ETAL 3,356,528

METHOD AND APPARATUS FOR DIFFUSION COATING OF METALS IN COILED STRIPS 3 Sheets-Sheet Filed Nov. l4, 1963 A. p W

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,4 lnvenlofs THOMAS G/aso/v 4/10 WILL/AM A. MGADAM Aliorm-y United States Patent M 3,356,528 METHOD AND APPARATUS FOR DIFFUSION COATING OF METALS IN COILED STRIPS Thomas Gibson, Motherwell, and William R. McAdam, Carlnke, Scotland, assignors, by mesne assignments, to Colvilles Limited, Glasgow, Scotland, a British company Filed Nov. 14, 1963, Ser. No. 323,750 Claims priority, application Great Britain, Nov. 15, 1962, 43,185/62 6 Claims. (Cl. 117-1071) ABSTRACT OF THE DISCLOSURE In a process for treating the surface of a flexible metal strip, the strip is co-wound with a cord on a bobbin to form interleaved coils so that the turns of the metal coil are held substantially uniformally spaced from one another by the cord. The coil is externally bound by a cord to prevent unwinding and the bound coil is set on end. Treating medium is packed into the uppermost end and the uppermost end closed by means of a cylindrical container inserted over the coil. The coil together with the containers are inverted; treating medium is packed into the now uppermost end; and the spacing cord is removed. The packed coil is heated.

This invention relates to the treatment of metals by a process of the kind comprising applying a coating or layer of granular or powdered solid treating or activating medium to the metal surface and heating the coated metal. Such granular or powdered solid treating or activating medium is referred to hereinafter and in the claims simply as the treating medium.

Examples of a process of the aforesaid kind are the well-known carburising process in which the surface of iron or steel is enriched with carbon by heating the metal in a pack of solid graphite treating medium; the chromising procss in which metals have their surfaces enriched with chronium by being heated in a pack of chromiferous treating medium; the aluminising process for enrichment of the metal surface with aluminium from a pack of aluminium-bearing treating medium; the sheradising process in which the enriching element of the treating medium is zinc; and the siliconising process in which the treating medium enriches the metal surface with silicon.

In a process of the aforesaid kind, it is important that all parts of the surface to be treated should be in contact with the treating medium during the thermal cycle of the treatment. Generally, there is a minimum thickness for the layer of treating medium in order to ensure an adequate supply of the enriching element for the surface. Preferably, a uniform layer of predetermined thickness is applied in order to achieve uniform enrichment over all parts of the surface, and in order to obtain maximum economy of the space available in the treatment furnace or oven.

An object of the invention is to provide for the convenient and efiicient treatment of a length of flexible metal strip, especially a long strip of relatively thin metal sheet material, by a process of the kind aforesaid.

Another object of the invention is to control in a simple manner the thickness and uniformity of the coating or layer of treating medium applied to the surface of the flexible metal strip.

Yet another object of the invention is to provide simple and compact apparatus for use in treating flexible metal strip by a process of the aforesaid kind.

According to the present invention, a process of the aforesaid kind as applied to a flexible metal strip includes the steps of winding the strip into a coil with its turns spaced substantially uniformly from one another, and

3,356,528 Patented Dec. 5, 1967 packing the treating medium into the space between the turns.

Preferably the process includes co-winding the strip with elongated flexible spacing means to form interleaved coils so that the turns of the metal coil are held substantially uniformly spaced from one another by the turns of the coiled spacing means, packing treating medium through one end face of the coil into the spaces between the turns, packing treating medium through the other end face of the coil into the spaces between the turns, and removing the spacing means.

Further according to the present invention, apparatus for use in treating the surface of a flexible metal strip with a treating medium comprises a bobbin for use in winding the strip into a coil and having its end plates detachable from its core to enable endwise packing of the coil with treating medium which enters between the turns of the coil on the core.

Apparatus embodying the invention will now be described by way of example with reference to the accompanying diagrammatic drawings in which:

FIG. 1 is a side view showing a coil-rewinding device;

FIG. 2 is a sectional plan view of a bobbin of the device;

FIG. 3 is a sectional side view showing the inter-turn spaces of one section of the rewound coil packed with treating medium;

FIG. 4 is a view similar to FIG. 3 showing the coil enclosed in an inverted pot; and

FIG. 5 is a view showing the other section of the coil filled with treating medium and the spacing cord being removed.

Referring to the drawings:

A long strip of flexible sheet metal to be treated is in the form of a coil 1 such as is generally supplied by commercial manufacturers of rolled metal sheet. If necessary, the strip has been degreased and pickled in a suitable chemical solution so that the surfaces of the strip are chemically clean and free of all rolling scale. Preferably, cold-reduced strip is used on account of its dimensional uniformity and of the superiority of its surface finish to that of hot-rolled strip.

The coil 1 of strip is re-wound by a device consisting of a bobbin 2 having a tubular cylindrical metal core or former 3 of which the axial length is equal to the width of the strip. At the ends of the former 3 are projecting metal pins 4 which fit loosely into corresponding holes 5 in the metal end plates 6 of the bobbin so that the end plates are detachable from the former 3. The end plates 6 are circular in shape and their diameter is slightly greater than the maximum diameter of the re-wound coil. The bobbin is mounted on a rotary spindle 9 which is suitably supported. A thrust collar 7 and a threaded nut 8 are fitted to the ends of the spindle 9 and clamp the circular end plates -6 tightly against the ends of the former 3 while enabling removal of the bobbin from the spindle.

As the strip is being re-wound on tot-he bobbin, there is co-wound with the strip a length of cord 10, preferably of circular cross-section, the diameter of the cord being equal to the required thickness of the coating or layer of treating medium. The cord 10 may be made from natural or synthetic fibres, or from strands of metallic wire, being sufiiciently flexible to follow the contours of the coiled strip without kinking. The cord 10 is thus interleaved with the turns of the coiled strip 1 and acts as a spacer which holds the turns a predetermined distance apart from one another. In the case of a relatively broad strip, a single cord may act as a pivot about which individual turns of the coil may rock through a small angle, and this would result in the spacing between adjacent turns of the coil becoming non-uniform and, in fact, may result in adjacent turns touching one another. Accordingly, in such cases, it is preferred to eo-wind with the coil two similar cords 10 so that the cords lie side-by-side in interleaved relationship with the coil. It has been found that by this means the distance between adjacent turns of the coil is maintained in complete uniformity.

When the re-winding has been completed, a sufiieient excess length of the spacing cord 10 is left to allow it to be drawn to the side of the coil at a later stage, as at 10A (FIG. '3), for subsequent withdrawal from the coil. A binding of metallic wire 11 is wrapped around the outside of the coil to prevent self-unwinding of the coil.

The bobbin containing the re-wound coil is withdrawn from the spindle 9 and is placed on a level surface (FIG. 3) with one end plate 6 resting flat on the surface. The upper end plate 6 is then withdrawn from the locating pins 4 of the bobbin former 3 without disturbing the coil.

A strip of flexible sheet metal 12 is wrapped around the outer periphery of the coil and protrudes above the edge of the coil to form an enclosing Wall 12A. The wrapping strip 12 is clamped to the coil by means of a metallic binding wire 13.

A treating medium 14 is poured into the dish formed by the end plate 6, the former 3, the coil 1, and the wrapping strip 12. The medium is packed into the spaces between the turns of the coil 1 until it reaches the spacing cord 10 and binding wire 11, and preferably some form of vibration is applied to the dish assembly in order to compact the medium and eliminate voids between the turns of the coil. The dish is filled until the level of the medium is flush with the top of the wall 12A.

A cylindrical metal pot 15 (FIG. 4) with a fiat base 16 is inverted and placed over the Wrapped coil, completely enclosing it. The inside of the flat, circular base 16 of the pot rests on top of the wall 12A, thus entrapping the medium 14 contained within the dish. The inside diameter of the pct 15 is slightly greater than the diameter of the end plate 6 so that the pot fits easily over the dish and drops over the plate 6. The assembly consisting of the half-filled dish and the pot is inverted, a clamping pressure being applied between the lower end plate 6 and the outside of the fiat base 16 of the pot 15 so that, during inversion, no treating medium escapes from within the confines of the assembly.

The end plate 6, now on top, is removed from the pins 4 of the bobbin former 3 (FIG. to expose the unfilled section of the dish which is then filled with treating medium 14. During filling, the loose end A of the spacing cord 10 is gripped and the cord is progressively Withdrawn from the coil in a spiral path, and simultaneously the dish-and-pot assembly is vibrated so that treating medium flows progressively into the space vacated by the cord. All voids are thus filled.

The treating medium 14 is compacted, preferably by vibration, into the dish-and-pot assembly until its level is flush with the top edge of the pot. The completely filled dish-and-pot assembly is now placed within the treatment furnace or oven for heat processing as required.

Thus, a completely uniform coating or layer of treating medium of predetermined thickness is quickly provided over all the surfaces of long strips of flexible sheet metal by a process which involves the use of simple and inexpensive apparatus. The coated metal is in a highly compact form so that the provision of a heating oven of great length and complexity is avoided. Moreover, the treating medium packed into the assembly maintains the turns of the coil against collapse and so enables treatment of thin metal sheet which would normally tend to collapse partially when in coil form.

Examples of the process will now be described.

Example 1 A coil of steel strip 250 feet long, 6 inches wide and .014 inch thick was chromised using the apparatus and process of this invention. The chemical composition of the steel was:

Percent Carbon 0.058

Manganese 0.30 Sulphur 0.020 Phosphorus 0.009 Iron Balance to The treating medium consisted of an intimate mixture of 9 parts by weight of ferro-chromium, 9 parts by weight of calcined bauxite and 1 part by weight of anhydrous chromous chloride. The chemical composition of the ferro-chromium was:

The particle size of the treating medium was from 60 to +200 mesh.

The thickness of the layer of treating medium between each turn of the coil was 0.04 inch.

The prepared coil was heated in an atmosphere of hydrogen in a controlled-atmosphere furnace to the temperature of 1,000 degrees centigrade and maintained at this temperature for 8 hours. It was then allowed to cool to room temperature in the furnace, the hydrogen atmosphere being maintained. Subsequently the coil was Withdrawn from the furnace and recoiled, the steel strip being passed through a brushing device to remove the l osely adhering particles of the treating medium.

Metallurgical examination revealed that the steel strip had a uniformly thick diffused zone, rich in chromium, over all parts of its surface. The depth of this zone was 0.0025 inch.

Example 2 A coil of steel strip 500 feet long, 4 inches wide and 0.009" thick was chromised by a procedure similar to that of Example 1. The chemical composition of the steel was:

Percent Carbon 0.055 Manganese 0.36 Sulphur 0.022 Phosphorus 0.012 Aluminium 0.083 Iron Balance to 100 After chromising, the depth of the uniformly thick diffused zone covering the complete surface of the steel strip was 0.0028 inch.

The steel treated in Example 1 was of the type known commercially as rimming steel, and that in Example 2 as killed or stabilised steel.

After chromising, the grain size of the rimming steel was found to be A.S.T.M. 1-2, and of the killed steel A.S.T.M. 3-4. Such grain sizes are relatively coarse and limit the commercial uses of the steel.

To overcome such limitations, the chromised steel strip was submitted to cold-reduction in a standard cold-reduction rolling mill. The reduction in the thickness of the strip varied between 10% and 75%, with a preferred range between 30% and 50%. The strip was then heated to a temperature between 600 and 650 degrees centigrade for a period of time between 30 minutes and 8 hours.

It was discovered that with 50% cold reduction and subsequent heating at 620 degrees centigrade for 1 hour, the rimming steel from Example 1 had an A.S.T.M. grain size 4-6, and the killed steel from Example 2 had an A.S.T.M. grain size 6-7.

We claim:

1. A process for treating the surface of a flexible metal st-rip, comprising co-winding the strip with elongated flexible spacing means to form interleaved coils so that the turns of the metal coil are held substantially uniformly spaced from one another by the turns of the coiled spacing means, externally binding the metal coil by a flexible band to prevent self-unwinding of the metal coil, setting the bound metal coil on end, packing treating medium through the uppermost end, closing said uppermost end, inverting the bound metal coil, packing treating medium through the now uppermost end, removing the spacing means from the metal coil, and heating the coated coil.

2. A process according to claim 1, wherein an end of the spacing means is left hanging from an end of the metal coil to facilitate subsequent removal of the spacing means.

3. A process according to claim 1, wherein the metal coil during packing with the treating medium is vibrated to compact the treating medium therein.

4. A process according to claim 1, wherein metal strip is of steel and following treatment is subjected successively to cold reduction in a rolling mill and heating.

5. Apparatus for use in treating the surface of flexible metal strip with a treating medium, comprising a bobbin for use in Winding the strip into a coil and having a core and circular end plates detachable from the core to enable endwise packing of the coil with treating medium, an open ended cylindrical wall having a diameter less than said circular end plates and a length greater than the sum of the axial length of the bobbin and the thickness of one of said end plates, the cylindrical wall being arranged, on the removal of one end plate, to sit on the other end plate and surround the coil of strip and a cylindrical container having a diameter greater than said end plates and a length equal to the sum of the length of said cylindrical Wall and the thickness of one of said end plates, said container serving to close the open top of the encircled coil to enable inversion of the coil during packing without loss of treating material.

6. Apparatus according to claim 5, including a rotary spindle for supporting the bobbin during Winding of the coil, and releasable clamping means on the spindle for retaining the bobbin on the spindle and simultaneously clamping the detachable end plates against the core.

References Cited UNITED STATES PATENTS 1,150,011 8/1915 Barker 242-1186 1,312,716 8/1919 Wise 117-22 2,409,384 10/1946 Peterson 148-155 X 3,114,539 12/1963 Wilson et a1. 263- 3,163,553 12/1964 Commanday et a1. 117-22 X 3,222,212 12/1965 Samuel et a1 117-48 X 3,257,227 6/1966 Seelig 117-66 ALFRED L. LEAVI'I'I, Primary Examiner.

I H. NEWSOME, Assistant Examiner. 

1. A PROCESS FOR TREATING THE SURFACE OF A FLEXIBLE METAL STRIP, COMPRISING CO-WINDING THE STRIP WITH ELONGATE FLEXIBLE SPACING MEANS TO FORM INTERLEAVED COILS SO THAT THE TURNS OF THE METAL COIL ARE HELD SUBSTANTIALLY UNIFORMLY SPACED FROM ONE ANOTHER BY THE TURNS OF THE COILED SPACING MEANS, EXTERNALLY BINDING THE METAL COIL BY A FLEXIBLE BAND TO PREVENT SELF-UNWINDING OF THE METAL COIL, SETTING THE BOUND METAL COIL ON END, PACKING TREATING MEDIUM THROUGH THE UPPERMOST END, CLOSING SAID UPPERMOST END, INVERTING THE BOUND METAL COIL, PACKING TREATING MEDIUM THROUGH THE NOW UPPERMOST END, REMOVING THE SPACING MEANS FROM THE METAL COIL, AND HEATING THE COATED COIL.
 5. APPARATUS FOR USE IN TREATING THE SURFACE OF FLEXIBLE METAL STRIP WITH A TREATING MEDIUM, COMPRISING A BOBBIN FOR USE IN WINDING THE STRIP INTO A COIL AND HAVING A CORE AND CIRCULAR END PLATES DETACHABLE FROM THE CORE TO ENABLE ENDWISE PACKING OF THE COIL WITH TREATING MEDIUM, AN OPEN ENDED CYLINDRICAL WALL HAVING A DIMAETER LESS THAN SAID CIRCULAR END PLATES AND A LENGTH GREATER THAN THE SUM OF THE AXIAL LENGTH OF THE BOBBIN AND THE THICKNESS OF ONE OF SAID END PLATES, THE CYLINDRICAL WALL BEING ARRANGED, ON THE REMOVAL OF ONE END PLATE, TO SIT ON THE OTHER END PLATE AND SURROUND THE COIL OF STRIP AND A CYLINDRICAL CONTAINER HAVING A DIAMETER GREATER THAN SAID END PLATES AND A LENGTH EQUAL TO THE SUM OF THE LENGTH OF SAID CYLINDRICAL WALL AND THE THICKNESS OF ONE OF SAID END PLATES, SAID CONTAINER SERVING TO CLOSE THE OPEN TOP OF THE ENCIRCLED COIL TO ENABLE INVERSION OF THE COIL DURING PACKING WITHOUT LOSS OF TREATING MATERIAL. 